This invention relates to electrostatic imaging and in particular, to a new and improved process and apparatus for improving the contrast in visual images produced by depositing toner onto an electrostatic image.
In the electronradiography process, an X-ray image of an object is converted into a visual image by absorbing the X-ray radiation and producing electrons and positive ions in an electric field, with the charges being selectively moved towards opposite electrodes to form an electrostatic charge image. A real time imaging system of the electronradiography type is shown in U.S. Pat. No. 3,965,352. In this type of system, the electrostatic charge image is formed on a surface exposed to a dielectric liquid with the toner particles suspended therein. When an appropriate electric field is produced in the system, toner particles are selectively attracted to the electrostatic charge image producing a toner particle image on a substrate which can be viewed by reflected light or scattered light. The process of forming the visual image is reversible by reversing the electric field, leaving the system ready for forming another electrostatic image and a subsequent visual image.
In either mode of viewing, there are stray light rays which deviate from the optimum illumination path because of interaction with internal surfaces of the apparatus and with interfaces between various optical components. These deviant rays illuminate reflective surfaces and light scattering points other than the toner particles, thus producing unwanted background radiation in the optical image or signal. This results in an undesirable reduction in the image contrast.
It is an object of the present invention to provide a new and improved process and apparatus for increasing the contrast in the resultant visual image of an electrostatic imaging system.